1. Field of the Invention
This invention relates to the subject of skeletal or porous metal catalysts. Methods of controlling the form and structure (i.e., surface area, particle size and shape, pore structure, surface and bulk composition) which control the ultimate performance of a skeletal type catalyst comprises the subject of the invention. This invention includes fabriccation techniques and the resultant skeletal catalysts.
2. Description of the Prior Art
The skeletal form of catalyst is described in numerous patents including U.S. Pat. Nos. 1,628,190; 2,384,501; 3,627,790 and 3,809,658. Briefly, this type catalyst is formed by the chemical leaching of an intermetallic compound formed between a catalytically active metal and a less noble metal. The leaching preferentially removes the less noble metal and produces a porous structure having a high surface area predominantly comprised of the catalytically active metal. The catalytically active metals include, but are not limited to, the transition metals. Intermetallic compounds between such a catalytically active element and a less noble (non-catalytic) element such as Al are usually employed.
Prior art fabrication techniques involve casting of intermetallic compositions followed by comminuting and leaching. Attempts to directly cast incongruently melting intermetallic compositions (such as those involving peritectic reactions) are usually not successful, resulting in a mix of phases rather than a single phase intermetallic structure.
In a different subject area, but one which relates to this invention, it is known that under certain solidification conditions an oriented microstructure may be produced in eutectic compositions. This is taught in U.S. Pat. Nos. 3,124,452; 3,528,808; 3,552,953; 3,554,817; 3,564,940 and 3,671,223 all of which are assigned to the assignee of the present invention.